1. Field
The disclosed embodiments relate to image producing devices and, more particularly, to a system and method for reducing motion quality defects while printing or copying an image.
2. Brief Description of Related Developments
Electrophotographic marking is typically performed by exposing a light image of an original document or image onto a uniformly charged photoreceptor. In response to the light image, the photoreceptor discharges so as to create an electrostatic pattern of the original document. Toner is attracted to the electrostatic pattern to form an image on the photoreceptor. A number of photoreceptors may be mounted on an imaging drum and the images may be transferred from the imaging drum, either directly, or after an intermediate transfer step, and fused onto a marking substrate or media, such as a sheet of paper.
The transfer and fusing may be accomplished by pinching the media between the imaging drum and a transfer roll. The point where the imaging drum and transfer roll are in contact with the media may be referred to as a nip. The media is pinched between the imaging drum and the transfer roll such that a fusing pressure is created in the nip, which may be accompanied by the generation or application of heat, to fuse the image to the media.
Other techniques may also be used for applying an image to an imaging drum or portion of an imaging drum for subsequent transfer to the media. For example, a direct marking technique may be used where a charged, colorless toner layer may be applied to the imaging drum. A non-contacting ink jet marking technology may be used to apply an ink jet image to the imaging drum, for example, thermal ink jet, acoustic ink jet, piezo ink jet, or any other type of suitable direct marking technique.
Regardless of the technique used to produce an image on the imaging drum, the image is generally transferred to the media by pinching the media between the imaging drum and the transfer roll, fusing or fixing the image to the media as mentioned above.
When the transfer roller is fully engaged with the imaging drum, it may apply a load in the range of approximately 500-700 lbs. in a relatively short period of time. The addition and removal of such a load in such a period of time may cause the velocity of the imaging drum to deviate, resulting in a transient rotational disturbance of the drum. Additionally, there may be a steady state velocity change due to the load. The inertia of the imaging drum and its control system may be large enough so that the control system""s closed loop bandwidth cannot accommodate these velocity deviations, resulting in image mis-registration, or other undesirable effects, referred to as motion quality problems.
Currently, when performing marking operations that require multiple passes, the processes of forming the image on the imaging drum and transferring the image to the media are performed sequentially. The imaging must be completed before beginning the transfer process because of the motion quality problems associated with engaging the transfer roller with the imaging drum after the image has been formed on the imaging drum. As a result, productivity is limited by performing the imaging and transferring operations in series. When using an imaging drum with more than imaging surface, also referred to as a pitch, the image formed on one pitch must be transferred before an image may be formed on another pitch.
The disclosed embodiments are directed to a method of maintaining a rotational velocity of an imaging drum in an image producing device. In one embodiment, a table is constructed of a drive current for a transfer roll for a plurality of first distances between the imaging drum with the transfer roll, and utilizing the table to control the transfer roll drive to maintain a substantially constant imaging drum rotational velocity at each of the plurality of distances.
Another embodiment is directed to constructing a table of a drive current for a transfer roll for a plurality of engagement and disengagement positions of the imaging drum with the transfer roll, and utilizing the table to control the transfer roll drive to maintain a substantially constant imaging drum rotational velocity during engagement and disengagement with the transfer roll.
A further embodiment includes measuring a drive current of the imaging drum, incrementally moving the transfer roll to engage and disengage the imaging drum, and adjusting a current set point of a transfer roll drive to maintain the measured imaging drum drive current at each incremental movement. This embodiment also includes recording the adjusted current set point for each incremental movement in a table, and utilizing the table to control the transfer roll drive current to maintain a substantially constant imaging drum rotational velocity during subsequent engagement and disengagement with the transfer roll.